Will Los Angeles bring its cougars back from the brink?

National Park Service biologist Jeff Sikich carries a tranquilized young male mountain lion back to a team waiting to attach a GPS tracking collar to the animal in the Santa Monica Mountains, in late 2012.

"They were going extinct," says Robert Wayne, the evolutionary biologist who oversees the DNA-testing lab at UCLA. "They had undescended testes, holes in their hearts, defective sperm." The Florida population only survived because they were, as Wayne puts it, "genetically rescued" in 1995 with the release of eight female panthers imported from Texas. Only the offspring of the imports have thrived.

The isolated cougars of the Santa Monicas don't need such a dramatic solution; other genetic strains roam not far away. Just 15 miles north of where P-19 is raising her kittens, space yawns open in the Santa Susana Mountains, which link to hundreds of square miles of contiguous habitat in the Los Padres National Forest. But to move that direction, animals have to cross all eight lanes of the 101 Freeway, which connects the cities of Los Angeles and Ventura.

Sikich takes me to a place on the 101 where there's natural habitat on both sides, the aptly named Liberty Canyon. From the north, the canyon funnels wildlife onto a lightly used road under the freeway; P-12 crossed here. But an animal making its way down the slope south of the freeway, a narrow channel of green through the housing tracts, would have to brave a vacant three-story office building to find that route. "We've had animals turn around here," Sikich says. "The ones that risk the freeway usually end up dead."

Biologists, wildlife advocates and the California Department of Transportation have long lobbied for an underpass here whose entrance would make sense to wildlife. It would cost $10 million, but it would offer a safe option for animals compelled to migrate north. It might have lured P-22 toward more promising lands than Griffith Park. And it might have opened up a route for the unnamed young lion that, on May 22, tested his boundaries and found himself stranded in a city.

That Tuesday morning, janitor Rogelio Rodriguez showed up for his pre-dawn shift at a downtown Santa Monica office building and heard a strange scratching sound. When he went to investigate, he saw a fawn-colored feline, six feet long and half again as tall, pawing on a wall just a few feet away. The animal turned around and saw Rodriguez, then ran past him into a courtyard. Rodriguez called the police.

Later blood tests revealed the lion came from the Santa Monicas. A young male, not quite 2 years old, he had likely wandered down during the night, crossing three miles of backyards or following the beach. He was now more trapped than when he started.

Wildlife agents first tried darting the lion, but the drug didn't take. Instead, the animal ran. Glass walls eight-feet high surround that courtyard, "but the thinking was that if he could get in, he could get out into the street," says assistant chief of California Fish and Wildlife Dan Sforza; pumas can spring to the top of 15-foot cliffs. Local police officers tried to hold the animal back with pepper spray, but when "he came toward the glass, the police shot him."

Bystanders were horrified. Blogs and comments overflowed with protests. But Seth Riley, the principal investigator on the Park Service study, says that the saddest part of the story came later, with the lion's DNA tests. "He had some unique genetic markers not seen in our other Santa Monica lions," he laments. "And he never got to pass them on."

Last year, the California Department of Transportation was turned down for a federal grant to fund the Liberty Canyon underpass. Riley insists the cost is justified. "These mountain lions are the ultimate challenge for conservation," he says. "If the system is able to sustain large carnivores, it says something good about the way we're able to conserve it." If it's not, the fragment of wilderness known as the Santa Monica Mountains will devolve into another large urban park.